In the prior art, generic devices for collision monitoring on a numerically controlled machine tool for machining a workpiece are known which comprise a collision monitoring unit for detecting a collision of machine parts of the machine tool when a measuring value detected by a collision sensor of the collision monitoring unit exceeds a collision limit value (for example, in a collision on the machine tool or when the workpiece is machined too vigorously), and a stop unit for stopping the at least one work spindle and the at least one feed axis of the machine tool when the collision monitoring unit detects a collision.
Such devices as a rule comprise a collision sensor such as, for example, a clip gauge which may be mounted particularly adjacent to the work spindle of the machine tool such as for example, on a milling head of the machine tool. The collision monitoring unit receives a measuring signal of the collision sensor via a signal input and is adapted to detect when the measuring value of the collision sensor exceeds a determined collision limit value.
In this case, the collision limit value of the prior art is predetermined by the manufacturer, for example, to a value of 20 g (g referring to the acceleration of gravity) and cannot be changed by the operator of the machine tool or a programmer of control data for the numerically controlled machine tool.
As soon as the collision monitoring unit detects that the measuring value of the collision sensor exceeds the predetermined collision limit value, a fast shutdown is performed on the machine tool via machine control, i.e. via the programmable logic controller (PLC), in which the drive of the work spindle and the drives of the feed axes of the machine tool are stopped to be able to prevent or at least reduce damage to the machine tool due to the detected collision. Upon detection of a collision by the collision monitoring unit, it is possible, for example, to trigger an emergency stop of the machine tool via the programmable logic controller or to initiate at least a quick stop of the work spindle and the feed axes as soon as the collision monitoring unit detects that the measuring value of the collision sensor exceeds the determined collision limit value. In this course, the drives of the work spindle and the feed axes are stopped and slowed down with as maximum an acceleration as possible, in particular before it can be detected at the machine control that the servo lag on the machine tool exceeds a limit value and before deformation occurs on machine parts of the machine tool.
In this case, the determined collision limit value, as mentioned above, is fixedly set by the manufacturer to a particular maximum acceleration value so that the shutdown of the drives of the work spindle and the feed axes and the emergency stop on the machine tool, respectively, is triggered independently of the machining process by means of a collision detection in dependence of the collision limit value predetermined by the manufacturer.